Integrated electro-optic analyzer

ABSTRACT

An integrated electro-optic birefringent analyzer is disclosed including an electro-optic birefringent medium whose birefringence varies as a function of an associated electric field and a first polarizing medium integrally structured with the electro-optic birefringent medium for detecting the polarization modulation imposed on radiation by the electro-optic birefringent medium.

United States Patent 1 Buchan 1 Jan. 30, 1973 [54] INTEGRATEDELECTRO-OPTIC ANALYZER [75] Inventor: William R. Buchan, Lincoln, Mass.

[73] Assignee: ltek Corporation, Lexington, Mass.

[22] Filed: April 21, 1971 [21] App]. No.: 135,979

OTHER PUBLICATIONS McGraw-Hill Encyclopedia of Science 81. Technology,Vol. 10(McGraw-Hill, N.Y., 1960) pp. 452453.

Primary ExaminerDavid Schonberg Assistant Examiner-Paul R. MillerAttorneyHomer 0. Blair, Robert L. Nathans, David E. Brook and Joseph S.landiorio [57] ABSTRACT An integrated electro-optic birefringentanalyzer is disclosed including an electro-optic birefringent mediumwhose birefringence varies as a function of an associated electric fieldand a first polarizing medium integrally structured with theelectro-optic birefringent medium for detecting the polarizationmodulation imposed on radiation by the electro-optic birefringentmedium.

5 Claims, 5 Drawing Figures INTEGRATED ELECTRO-OPTIC ANALYZERCHARACTERIZATION OF INVENTION polarization modulation imposed onradiation by the electro-optic birefringent medium.

FIELD OF INVENTION This invention relates to an integrated electro-opticstructure for reading out information present in the form of variationsin intensity of an electric field.

BACKGROUND OF INVENTION Recent developments in the field ofelectro-optic readout apparatus and techniques indicate that informationpresent in the form of variations in the intensity of an electric fieldmay be read out using a medium that exhibits electrically inducedbirefringence. In such techniques an electro-optic birefringent mediumis associated with an information bearing electrical field. Suchinformation bearing fields may be those established by corona dischargeon a dielectric material or those present in photoelectrets, orthermoelectrets or in any other form. Readout is accomplished byassociating the electro-optic birefringent medium with the electricfield so that the electric field is established across the medium, andthe medium is exposed to polarized radiation. The birefringence of themedium causes the polarized radiation to become elliptically polarized;the ellipticity is a function of the birefringence of the medium whichis in turn a function of the intensity of the electric field. If forexample, the medium is exposed to vertically polarized radiation areasof the medium subjected to a low intensity electric field have lowinduced birefringence and so produce elliptical polarization of theradiation wherein the ellipse is vertically elongated and contains along vertical component but a small horizontal cross component. Incontrast, areas of the medium subjected to a high intensity electricfield have high induced birefringence and so produce ellipticalpolarization of the radiation wherein the ellipse is horizontallyelongated and contains a short vertical component and a long horizontalcross component. An analyzer oriented with its plane of polarizationparallel to the horizontal plane detects the horizontal componentsrepresentative of the pattern of variation of the intensity of theelectric field. Generally the readout apparatus includes anelectro-optic birefringent medium, a source of polarized radiation whichmay comprise a source of unpolarized radiation plus a polarizingelement, and an analyzer which may be a second polarizing element whosepolarization axis is crossed relative to the axis of polarization of theinput radiation. Such apparatus is usually arranged with its componentsin spaced relation so that substantial space is required to accommodatethe whole apparatus. Further, skilled personnel and special equipmentmay be required to set up and align such apparatus.

SUMMARY or INVENTION It is therefore an object of this invention toprovide a small, rugged, simple, compact electro-optic birefringentreadout apparatus.

It is a further object of this invention to provide such an apparatuswhich is preassembled and so needs no special skills or tools toassemble.

It is a further object of this invention to provide such an apparatuswhich may be used in ordinary optical equipment.

It is a further object of this invention to provide such an apparatuswhich includes the necessary elements in an integrated structure.

The invention may be accomplished by an integrated electro-opticbirefringent analyzer including an electro-optic birefringent mediumwhose birefringence varies as a function of an associated electricfield. A polarizing medium integrally structured with the electro-opticbirefringent medium detects the polarization modulation imposed onradiation by the electro-optic birefringent medium.

DISCLOSURE OF PREFERRED EMBODIMENT Other objects, features andadvantages will occur from the following description of a preferredembodiment and the accompanying drawings, in which:

FIG. 1 is a diagram showing a method and apparatus for establishing aninformation bearing electric field in a device.

FIG. 2 is a diagram showing a method and apparatus for reading out theinformation present in the electric field in the device of FIG. 1.

FIG. 3 is an alternative form of the device shown in FIGS. 1 and 2.

FIG. 4 is a diagram of an integrated electro-optic birefringent analyzeraccording to this invention.

FIG. 5 is a diagram of an alternative construction of the integratedelectro-optic birefringent analyzer of this invention.

Typically, an information-bearing electric field may be establishedusing a device 10, FIG. 1, including a photoconductor medium, layer 12,and a dielectric medium, layer 14, between a pair of electrodes 16 and18 which are selectively connected in series with either shorting lead20 or battery 22 by means of switch 24. Electrode 16 is transparent andelectrode 18 may or may not be transparent. Information-bearingtransparency 26 having a low density upper portion 28 and a high densitylower portion 30 is illuminated by radiation from source 32. The lessintense radiation passing through the higher density lower portion 30 oftransparency 26 renders section 34 of photoconductive layer 12 slightlyconductive and the more intense radiation passing through the lowerdensity upper portion 28 of transparency 26 renders section 36 ofphotoconductive layer 12 more conductive. Thus with switch 24 connectedacross battery 22 as shown, the positive charges at electrode 16 passeasily through upper section 36 to the boundary of layer 14 whereas thepositive charges proximate the lower section 34 meet greater resistance.If switch 24 is not opened the charge pattern across the device 10 willremain as shown in FIG. 1. Alternatively, switch 24 may be moved to theposition in which it connects to lead 20 whereby electrodes 16 and 18are shorted together. This results in the dissipation of the charges inelectrode 16 proximate section 34 so that only the charges in section 36proximate the boundary of layer 14 remain. The period during which afield, once established, will remain present in device depends upon therelative resistances and capacitances of layers 12 and 14. If thecapacitances and resistances of both layers are high, the charge will bestored for a significant period of time which may extend for hours oreven days and so device 10 may be used as a storage medium. If thecapacitances and resistances of layers 12 and 14 are relatively low thenthe charge will be dissipated rather quickly and device 10 may be usedin real time applications where only momentary presence of the field isnecessary.

The information present in the electric field established in device 10may be read out by associating an electro-optic birefringent medium,layer 40, FIG. 2, with device 10 shown without electrodes 16 and 18. Themore intense electric field in section 36 of photoconductor layer 12results in a greater electrically induced birefringence in upper section42 of layer 40, and the lower intensity electric field across the lowersection 44 of layer 40 results in a lesser degree of birefringence insection 44. Readout may be accomplished using radiation from source 46polarized in the vertical plane, arrow 48, by a polarizing element 50.The polarized radiation may be circularly polarized instead of planepolarized and element 50 may be eliminated if source 46 supplies thepolarized radiation.

The radiation subject to the greater induced birefringence of section 42produces elliptically polarized radiation, ellipse 52, having a largehorizontal cross component 54 and a smaller vertical component 56.Radiation subject to the lesser induced birefringence of section 44produces elliptically polarized radiation, ellipse 58, having a largevertical component 60 and a small horizontal cross component 62. Thiselliptical polarization modulation of the radiation may be detected by acrossed polarizer or analyzer 64 which may be a polarizing elementsimilar to element 50 but oriented with its polarization axis orthogonalto that of element 50 as indicated by arrow 48. Analyzer 64 detects onlycross components 54 and 62 to produce a pattern at sensor 66 which is arepresentation of the pattern of information present in transparency 26.The representation resulting from the detection by analyzer 64 is apositive of the information. If analyzer 64 were oriented with its axisof polarization parallel to that of element 50, then the representationdetected by it would be a negative. If electro-optic birefringent medium40 is also a dielectric medium then layer 40 may be substituted fordielectric layer 14 in device 10 so that layer 40 acts as both anelectrical blocking layer to permit an electric field to be establishedin device 10 and subsequently performs as an electro-optic birefringentmedium to enable readout of device 10.

Alternatively, both the electro-optic birefringent medium and thephotoconductor medium may be embodied in one layer 70 in combinationwith a dielectric layer 72 in device 74, FIG. 3. Exposure of thephotoconductor layer 70 to radiation in the same manner asphotoconductor layer 12 was exposed in FIG. 1 results in the same chargedistribution as occurs in FIG. 1. Thus the higher intensity radiationincident on upper section 76 of layer causes the charges to penetratelayer 70 to the boundary of dielectric layer 72 more readily than inlower section 78 subject to the less intense radiation. However, indevice 74 since layer 70 is both the photoconductor medium and theelectro-optic birefringent medium, the penetration of the chargesthrough section 76 results in a less intense electric field acrosssection 76 whereas the lesser penetration of the charges through section78 results in a stronger field across section 78. Therefore the inducedbirefringence of section 78 is greater than that of section 76 and theelliptical polarization of radiation transmitted by section 78 isgreater than the elliptical polarization of radiation transmitted bysection 76.

The radiation used to read out the information present in the electricfield by means of the electrooptic medium may be transmitted completelythrough the medium or may be reflected back through it. The radiationused to expose the photoconductive medium and that used to read out theelectro-optic medium need not be visible light.

Serial as well as parallel readout may be performed by scanning theelectro-optic medium with a beam of radiation. Similarly, thephotoconductor medium may be exposed serially as well as in parallel andthe photoconductor medium may be replaced by some other means forapplying an electric field to the electro-optic medium such as adielectric storage tape or a scanning electron beam.

The electro-optic medium may be formed of DKP, DKDP, or lithium niobate,and the photoconductor layer may be formed of amorphous zinc sulfide,zinc selenide, zinc telluride, or cadmium sulfide. Or both theelectro'optic birefringent medium and photoconductor medium may bepresent in a single material such as cubic zinc sulfide, zinc selenide,or zinc telluride, and combined with a dielectric blocking layer such aspolystyrene or SiO In accordance with this invention an analyzer such asanalyzer 64, FIG. 2, which also has dielectric properties is combined inan integral structure with an electrooptic photoconductor layer toproduce a single rugged integrated structure which can serve both asmeans to support an electric field representative of information and asmeans for reading out the information present in that electric field.

In one embodiment, device 80, FIG. 4, includes an electro-opticphotoconductor medium, layer 82, combined with a dielectric blockingmedium, which is also an analyzer for polarized radiation, layer 84.Layer 82 may be, for example, cubic zinc sulfide, and layer 84 may bemade of Polaroid sheet polarizer, arranged between two electrodes 86 and88. During a read in operation device 80 is exposed through electrode 86to radiation whose intensity varies in a pattern representative of someinformation. This pattern of radiation intensity causes thephotoconductor medium in layer 82 to assume a similar pattern ofconductance. An electric field is established in device 80 by thecharges moving from electrode 86 through the photoconductor medium inlayer 82 in a pattern similar to the conductance pattern established inthe photo-conductor medium, layer 82. Dielectric properties of layer 84function to prevent any charges migrating through the photo-conductormedium of layer 82 from reaching electrode 88,

thereby maintaining a charge separation which establishes the electricfield in device 80. During readout, when polarized radiation is suppliedthrough electrode 86 to the electro-optic medium of layer 82, thatpolarized radiation is elliptically polarized by the electro-opticmedium of layer 82 to an extent dependent upon the intensity of theelectric field across the electro-optic medium of layer 82. Thepolarizing or analyzing property of layer 84 acts to select onecomponent of the elliptically polarized radiation transmitted byelectro-optic layer 82 to detect the modulation introduced to thatpolarized radiation by the electro-optic medium under influence of theelectric field. Thus, in one device 80 there is contained all thenecessary elements for reading in and reading out information. Thephotoconductor medium, the electro-optic medium, the dielectric medium,the analyzing medium and the electrodes are contiguously, compactlyformed in an integral structure which is simple, rugged and requires nospecial aligning techniques of the optical elements for its operation.Further, device 80 may be made suitably shaped and sized to fit inexisting optical equipment such as slide projectors and the like.

A similar device 80' is shown in FIG. 5 where like parts have been shownwith like reference numerals primed with respect to FIG. 4. ln device 80the electro-optic and photoconductor mediums, layer 82', are arrangedbetween two dielectric polarizing mediums 84' and 84" within electrodes86' and 88. In device 80 electro-optic photoconductor layer 82 may becubic zinc sulfide and dielectric polarizing layers 84 and 84" may beformed of Polaroid sheet polarizer material. The use of two dielectricpolarizing layers 84', 84" in device 80' provide two significantadvantages. First, it incorporates both the polarizing element such aselement 50, FIG. 2, and the analyzing element such as element 64, FIG.2, in one simple, rugged integrated structure with the electro-opticphotoconductor medium. Layer 84" permits an unpolarized radiation sourcesuch as source 46, FIG. 2, to be used to read out the informationpresent in the electro-optic photoconductor layer 82' without therequirement of the usual external polarizing element and layer 84" doesnot interfere with the exposing radiation source which initiallyestablishes the electric field in device 80'. Second, the use of adielectric layer on either side of the electro-optic photoconductorlayer permits the electric field to be established across that layer ineach of the two possible directions. That is, either electrode 86' orelectrode 88 may be connected to the positive terminal of the battery orother energizing source. Previously, when only one dielectric layer wasused, it was necessary to connect the positive terminal of the battery22, FIG. 1, to the electrode 16 adjacent the photoconductor layer andthe negative terminal of battery 22 to the electrode adjacent thedielectric layer 14. For example, in the diagram of FIG. 1 if thepolarity of battery 22 were reversed the supply of electrons provided atelectrode 16 would be injected into the photoconductor material of layer12 causing it to respond as a typical semiconductor and becomeconducting so that no meaningful electric field representative ofinformation could be established.

Other embodiments will occur to those skilled in the art and are withinthe following claims:

What isclaimed is: 1. An integrated electro-opt1c storage device andanalyzer comprising:

an electro-optic birefringent medium whose birefringence varies as afunction of an associated electric field;

a photoconductor medium whose conductance varies as a function of theintensity of incident radiation thereon;

a first dielectric polarizing medium integrally attached to one face ofsaid electro-optic birefringent medium for detecting the polarizationmodulation imposed on radiation by said electro-optic medium; and,

a second dielectric polarizing medium integrally attached to saidphotoconductor medium to polarize incident light to said storage andanalyzer device.

2. A storage and analyzer device of claim 1 wherein said photoconductormedium and said electro-optic birefringent medium are included in thesame material.

3. A storage and analyzer device of claim 1 wherein said photoconductorand said electro-optic birefringent medium are each included in aseparate layer of material.

4. A storage and analyzer device of claim 1 further including means toimpose an electric field across said device.

5. A storage and analyzer device of claim 4 wherein said means forimposing includes a pair of electrodes spaced on opposite sides of thedevice, said electrodes being connected to a source of electricalpotential.

1. An integrated electro-optic storage device and analyzer comprising:an electro-optic birefringent medium whose birefringence varies as afunction of an associated electric field; a photoconductor medium whoseconductance varies as a function of the intensity of incident radiationthereon; a first dielectric polarizing medium integrally attached to oneface of said electro-optic birefringent medium for detecting thepolarization modulation imposed on radiation by said electro-opticmedium; and, a second dielectric polarizing medium integrally attachedto said photoconductor medium to polarize incident light to said storageand analyzer device.
 1. An integrated electro-optic storage device andanalyzer comprising: an electro-optic birefringent medium whosebirefringence varies as a function of an associated electric field; aphotoconductor medium whose conductance varies as a function of theintensity of incident radiation thereon; a first dielectric polarizingmedium integrally attached to one face of said electro-opticbirefringent medium for detecting the polarization modulation imposed onradiation by said electro-optic medium; and, a second dielectricpolarizing medium integrally attached to said photoconductor medium topolarize incident light to said storage and analyzer device.
 2. Astorage and analyzer device of claim 1 wherein said photoconductormedium and said electro-optic birefringent medium are included in thesame material.
 3. A storage and analyzer device of claim 1 wherein saidphotoconductor and said electro-optic birefringent medium are eachincluded in a separate layer of material.
 4. A storage and analyzerdevice of claim 1 further including means to impose an electric fieldacross said device.